Dense star polymers and dendrimers

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS In the dense star polymers of the present invention, the core is covalently bonded to at least one core branch, preferably at least two, most preferably at least three, core branches with each core branch having a calculated length of at least 3 Angstrom units (A), preferably at least 4 A, most preferably at least 6 A.
These polymers preferably have an average of at least 2, more preferably at least 3 and most preferably at least 4 terminal groups per polymer molecule.
Preferably, the core branches have a dendritic character, most preferably an ordered dendritic character as defined hereinafter.
The dense star polymers of this invention preferably have two-dimensional molecular diameters in the range from about 12 to about 2000 Angstrom units (A), more preferably from about 25 to about 500 A and most preferably from about 250 A.
For the purpose of this invention, a two-dimensional molecular diameter is determined by the following electron microscopic method.
First, the terminal groups of dendrimers are connected to anionic moieties (e.
g.
, by hydrolysis of the terminal ester moieties of polyamidoamine dendrimer in half generation state).
The anionic dendrimer molecules are then neutralized with stoichiometric amounts of alkali metal hydroxide.
A dilute aqueous solution (e.
g.
, about 0.
5 weight percent of the neutralized dendrimer in water) of the dendrimer is placed on a beryllium grid (.
about.
1.
5 millimeter diameter puddle) and allowed to evaporate.
The dendrimer often exhibits dendritic-like crystalline growth during the evaporation process.
The diameter of the dry dendrimer molecules in two-dimensional state are then measured by electron microscopy and found to correspond closely, e.
g.
, within 15 percent, to the diameters predicted by scaled Corey-Pauling molecular models.
Such measurements are readily made using a JEM-1200 EX Electron Microscope sold by JEOL Corporation using CTEM techniques on a beryllium grid coated with 50 A carbon.
The dense star polymers of this invention preferably have three-dimensional molecular diameters in the range from about 6 to about 1000, more preferably from about 10 to about 250, most preferably from about 25 to about 125 Angstrom units